如何在Racket中使用按键功能？

Question

我正在尝试制作门模拟器。通过使用钥匙，我可以改变门的状态，我查看了 Racket 中的文档。主要讲的是“上”“下”“左”“右”等一些常用键。我想问一下如何自定义按键。这是我的代码：

(define DOOR-OPEN-iamge)

(define DOOR-CLOSED-image)

(define DOOR-LOCKED-image)

(define DS-OPEN "open")

(define DS-CLOSED "closed")

(define DS-LOCKED "locked")



(define (door-simulator initial-ds)

  (big-bang initial-ds

    [to-draw draw-ds]
 
   [on-key change]))

(check-expect (draw-ds DS-OPEN) DOOR-OPEN)

(check-expect (draw-ds DS-CLOSED) DOOR-CLOSED)

(check-expect (draw-ds DS-LOCKED) DOOR-LOCKED)

(define (draw-ds ds)

  (cond

    [(string=? ds DS-OPEN) DOOR-OPEN]

    [(string=? ds DS-CLOSED) DOOR-CLOSED]

    [(string=? ds DS-LOCKED) DOOR-LOCKED]))

;门状态键

;"o"-关门 => 开门

;"c"-开门 => 关门

;"l"-关门 => 门锁

;"u"-门锁 => 门开

(check-expect (change DOOR-CLOSED) DOOR-OPEN)

(check-expect (change DOOR-OPEN) DOOR-CLOSED)

(check-expect (change DOOR-CLOSED) DOOR-LOCKED)

(check-expect (change DOOR-LOCKED) DOOR-OPEN)

(define (change w a-key)

  (cond

    [(key=? a-key "o")  (draw-ds w)]

    [(key=? a-key "c") (draw-ds w)]

    [(key=? a-key "l")    (draw-ds w)]

    [(key=? a-key "u")  (draw-ds w)]))

另外，关键部分的check-expect没有起作用。不过我应该为那部分使用什么函数或变量。

Answer 1

需要这些库（planetcute只是包含了一些用于绘图的图片，您可以稍后删除它）：

(require 2htdp/planetcute)
(require 2htdp/universe)
(require 2htdp/image)

前六个定义不会改变，我只是添加了一些来自planetcute的图片：

(define door-open chest-open)
(define door-closed chest-closed)
(define door-locked chest-lid)

(define ds-open "open")
(define ds-closed "closed")
(define ds-locked "locked")

door-simulator 的定义不会改变：

(define (door-simulator initial-ds)
  (big-bang initial-ds
    [to-draw draw-ds]
    [on-key change]))

draw-ds 将状态转换为图片并使用 place-image:

将其绘制到背景

(define (ds->image ds)
  (cond ((string=? ds ds-open) door-open)
        ((string=? ds ds-closed) door-closed)
        ((string=? ds ds-locked) door-locked)
        (#true door-open)))

(define bg (rectangle 500 500 "solid" "white"))

(define (draw-ds state)
  (place-image (ds->image state)  50 50 bg))

函数 change 不会调用 draw-ds，而只是 returns 新状态，基于当前状态和键：

(define (change state a-key)
  (cond
    [(and (key=? a-key "o")
          (string=? state ds-closed))
     ds-open]
    [(and (key=? a-key "c")
          (string=? state ds-open))
     ds-closed]
    [(and (key=? a-key "l")
           (string=? state ds-closed))
     ds-locked]
    [(and (key=? a-key "u")
          (string=? state ds-locked)) ds-open]
    (#true state)))

您可能需要重新排序这些定义，然后使用 (door-simulator ds-closed) 启动动画并按一些键（o、c...）。

如何在Racket中使用按键功能？

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